This invention relates to an electric stapler.
There are two types of electric staplers has: one using staples formed into a gantry shape beforehand; and the other having a forming plate for bending staples into a gantry shape before supplying them to a driver. In any one of these types, however, a staple magazine holder is placed above a table with which sheets of paper to be bound are loaded, and the table or the staple magazine holder is driven to move up and down. Then the paper is clamped between the staple magazine holder and the table, and a driver support member fitted with the driver is driven by a driver hoist mechanism to move from an upper standby position downward so that the staple on the staple guide of the staple magazine holder is driven into the paper.
The staple passed through the paper is caused to strike against a clincher plate on the table and is bent into shape along guide grooves formed in the clincher plate. Rotary clinchers in place of fixed type clincher plate may otherwise be provided in order to bend the staple flat by driving the clinchers to turn after the staple is driven-in. This is called a flat clinch type electric stapler.
In the aforementioned electric stapler, the driver is coupled to a motor via cams and levers and reciprocates between the upper standby position and the lowest point. However, various inconveniences occur when an error at the lowest point exceeds an allowable value due to the tolerance of each component part and assembling precision. In other words, when the lowest position is situated above a proper one, the striking force of the driver becomes insufficient, thus lowering the staple clamping performance. When the lowest position is lower than such a proper one, the drive is caused to excessively press the staple and paper and the problem is that an overload is applied to the driver driving mechanism.
Since the height of the lowest position in the driver unit of a typical conventional electric stapler is not adjustable, adjusting work such as the replacement of the driver is needed when an error in the lowest position exceeds the allowable value. The trouble and time necessary for assembling and maintenance work is a problem.
Furthermore, the position of a driver for use in striking staples has to be in agreement with the positions of clinchers for bending the legs of the staple thus ejected by the driver in a stapler. However, there are more elements in clincher-to-driver positional errors in the case of an electric stapler than those in a manual stapler because the electric stapler has a complicated driver mechanism and a larger number of parts. Particularly in a flat clinch type electric stapler in which the legs of staples are bent by means of pivotal clinchers, a slight positional error may cause defective clinching to occur, thus narrowing an allowable error range.
As a typical conventional electric stapler is not equipped with a clincher-to-driver position adjusting means, the problem is that extreme precision is required during machining and assembling in order to limit an error to a predetermined value or smaller.
With respect to a staple cartridge, in a conventionally known staple detecting unit, a sensor for detecting the presence or absence of staples in the staple cartridge is provided so that no-load running is prevented by breaking a staple driving circuit when the remainder of staples is running low.
Such a sensor in the staple detecting unit is mounted in the cartridge holder of the electric stapler and in the case of a type in which a sensor like a photointerrupter or an microswitch is switched on and off by an actuator, the actuator is projected into the staple passage of the staple cartridge and brought into contact with a staple.
When the end of the staple passes by the actuator, the actuator turns to reverse the output of the sensor and the driving circuit is cut off to establish a start suspending condition.
The rotational quantity of the actuator at the time the staple passage is detected is equal to the thickness of a staple wire and because the sensor is turned on and off by a very small rotational quantity, extreme accuracy is required for machining and assembling the staple cartridge, the cartridge holder and the actuator.
Although some of the staple detecting units are provided with a non-contact sensor such as a photosensor in a cartridge holder, they tend to lack stability in detecting a staple as the threshold value of the sensor is caused to fluctuate by the slight displacement of the relative position between the staple in the staple cartridge and the sensor.
Among electric staplers whose staple feeding mechanisms are designed to feed staples by means of a longitudinally reciprocating feed pawl or an endless belt, a feed-pawl type staple feeding mechanism is provided with a check pawl for preventing staples from moving back in its staple cartridge.
Such a check pawl is usually installed on the downstream or upstream side of the feed pawl. In any one of these types, however, no staples can be fed by the feed pawl any longer at a point of time the last linked staple is fed forward by the feed pawl after the staples in the cartridge are totally consumed. Consequently, a few staples out of those ranging from the head to the last one within the staple cartridge become unusable.
It has heretofore been common practice to replace the staple cartridge and to discard the used one when the feeding of staples becomes impossible. If, therefore, the staple cartridge is made repeatedly usable by having it replenished with staples, it will be considered contributable to saving resources and protecting the natural environment.
When a staple cartridge of such a type that a check pawl is disposed on the downstream side of a feed pawl and is replenished with new linked staples, however, the head portion of a newly supplied staple sheet is brought into contact with the rear end portion of the remaining staple sheet in the cartridge and the newly supplied staple sheet will not engage with the check pawl on the downstream side of the feed pawl. Consequently, the newly supplied staple sheet together with the feed pawl will repeatedly move back and forth and no staples can be supplied to the driver portion.
In the case of a staple cartridge with the check pawl arranged on the upstream side of the feed pawl, further, newly supplied staples can be made to engage with the check pawl on the condition that staples are supplied to the cartridge that has consumed its staples until the feeding of them becomes impossible. After the end of the staple sheet passes by the check pawl, there develops another problem arising from causing the staples connected together with an adhesive to be severed by the longitudinal reciprocating motion of the feed pawl, to be fed unstably or non-conformably, or otherwise having the staple cartridge clogged therewith
Referring to FIGS. 23A to 25B, several kinds of conventional staple supporting units are shown. In FIG. 23A, reference numeral 341 denotes a staple pusher; 342, a driver; 343, a forming plate in the form of a gantry; 344, a staple guide; and a reference symbol S, a linked staple sheet.
The staple pusher 341 placed under the staple guide 344 is longitudinally slidably mounted on a base (not shown), urged by a spring (not shown) in the direction of a front-end plate and as shown in FIG. 23A, forced to contact the front-end plate 345. A projected portion 341a slightly narrower than the central recessed portion of the forming plate 343 is formed in the front center of the staple pusher 341, and the upper front edge portion of the staple pusher 341 is chamfered over the whole width. Moreover, a projected portion 344a in agreement with the forming dimensions of a staple is projected forward in the front central portion of the staple guide 344, and both sides of the linear staple are bent into a gantry shape by the forming plate 343 along the respective sidewalls of the projected portion 344a of the staple guide 344.
A recess 345a substantially equal in width to the staple subjected to forming is formed in the center of inner sidewall of the front-end plate 345, and the formed staple is pressed by the staple pusher 341 into the recess 345a and held by the front-end plate 345 and the staple pusher 341.
FIGS. 23A and 23B show the standby state wherein a first staple S1 and one S2 on a second row have already been formed into a gantry shape, and the first one S1 stays in the recess 345a of the front-end plate 345.
As shown in FIGS. 24A and 24B, the driver 342 and the forming plate 343 are integrally moved down and simultaneously when the first staple S1 is struck by the driver 342 and starts penetrating into an object, both lateral sides of a liner staple S3 on a third row are pressed down by the forming plate 343 and bent along both the lateral sidewalls of a protrusion 345a of the staple guide 344. Further, the driver 342 and the forming plate 343 press the chamfered upper edge portion of the staple pusher 341 so as to move back the staple pusher 341. As shown in FIGS. 24A and 24B, further, the driver 342 and the forming plate 343 are moved down up to the lowest point, whereby the driving and forming of the staple are simultaneously completed.
When the driver 342 and the forming plate 343 are moved up subsequently, the whole linked staple sheet S is moved forward by a feed mechanism, and the first gantry-shaped staple is inserted in the recess 345a of the front-end plate 345. Then the staple pusher 341 is moved forward, so that the gantry-shaped staple is clamped between the front-end plate 345 and the staple pusher 341.
During the aforementioned drive-in stroke, it is desirous that the driver and the forming plate are brought into contact with the staple at the same time and when the forming plate comes into contact with the staple pusher earlier than the driver, the staple pusher is moved back before the staple is driven into the object and the staple may tilt and buckle in posture.
When the driver otherwise comes into contact with the staple pusher earlier than the forming plate, the staple pusher is moved back before the forming, which causes non-conforming forming. Although it is therefore attempted to design a staple pusher so that a driver and a forming plate are simultaneously brought into contact with a staple pusher, forming accuracy is hardly controllable and the problem is that above-described instability due to variation with time tends to occur.